How can I avoid destructuring and restoring everything?

For context, I'm working on the typescript type engine and I'm trying to handle code like

export function foo() {
    return a;

export const a = 5, b = foo();

While validating types, I need &mut reference to ast nodes because of .d.ts files.

So I defined a validator trait like the below.

pub trait Validate<T: ?Sized> {
    type Output;
    fn validate(&mut self, node: &mut T) -> Self::Output;

I'm using ast nodes ( from the swc project, and Validate is implemented per each node types.

To handle the code above, I should validate the function foo after the variable b, but after the variable a.
With the current design, I can't do so within Validate<VarDecl> obviously.

I thought long and hard about how to solve this problem, and I got a solution.
It can be implemented by converting all statements into kind of RefCell<StmtWrapper> and tracking the index of variable declarator with StmtWrapper in Validate<Vec<Stmt>>.

But destructuring and restoring everything is really cumbersome and I want to know if there's a better way.